Heart disease is the number one cause of death in the United States accounting for one in every four deaths. Coronary heart disease is the most common type, causing the deaths of over 400,000 people in 2005. In coronary heart disease, one or more coronary arteries become occluded. The subsequent lack of oxygen and nutrients often result in permanent death of a section of heart muscle. This reduces the ability of the heart to pump blood effectively. Despite the body's compensatory measures, in many patients there is a steady decline in cardiac function until failure occurs due to a lack of native myocardial regenerative ability. Several investigators have evaluated using adult human mesenchymal stem cells (hMSCs) to repair the damaged heart muscle, via systemic infusion, direct heart infusion or by incorporation into biodegradable scaffolds. These technologies, while showing promise, are limited in their effectiveness in that: 1) systemic infusion does not target the specific damaged area of the heart, potentially leading to adverse off-target effects, 2) direct infusion does not prevent migration of the hMSCs, again potentially resulting in off-target effects and 3) use of biodegradable scaffolds for hMSC containment does not permit device removal if required.
In addition, electronic pacemakers are readily available devices that are used to solve a variety of heart problems, extending from simple heart rate and rhythm problems to complete heart failure. Even though these devices are proven to be effective, they still have a variety of limitations. Limitations include the pacemaker's battery life, sensitivity to magnetic fields, and lead failure. These drawbacks require that a patient undergo repeated operations to replace the battery; they also inhibit the patient's ability to undergo other tests such as MRIs and CT Scans. Furthermore, there are also complications related to the implantation of the pacemaker. For instance, if the pacemaker leads are improperly placed, it can cause the wrong parts of the heart to contract, resulting in inefficient pumping and in severe cases, death. Perhaps the greatest disadvantage associated with the electrical pacemaker is that it lacks the ability to provide an appropriate cardiac response when the patient is exercising or is experiencing a strong emotional reaction.
Biological pacemakers are being developed as an alternative to these electrical pacemakers with the hope of mimicking the natural pacemaker and overcoming some of the electronic pacemaker's limitations. By utilizing stem cells as a biological pacemaker, they will be capable of providing an appropriate cardiac response to exercise and emotions since the cells can react to the physiological changes in the body. Also, a biological pacemaker would not contain batteries or leads; therefore such a device is not sensitive to magnetic fields. This would provide the patient with a better alternative to cure their heart condition. Although stem cells have good qualities that allow them to be ideal for engineering biological pacemakers, there are some risks associated with them. One of the biggest risks is stem cell migration. If these undifferentiated cells were to migrate to other areas of the heart, they could cause problems like fibrillation, beating of non-cardiac muscle tissue, or cancer.